1. Field of the Invention
The present invention relates to an apparatus for winding and unwinding at least two cables, and to a device embodying such an apparatus wherein the cable connects a part of the device to electrically operated components mounted on the device, which can be displaced relative to a part of the device as the cables wind and unwind.
2. Description of the Prior Art
German PS 40 19 513, corresponding to U.S. Pat. No. 5,145,390, discloses an apparatus with a rotatable drum for winding and unwinding a cable. The drum has an outer hollow cylindrical drum surface which is rotatably mounted about an inner hollow cylindrical drum surface that is stationary relative to the outer drum surface. The outer drum surface accepts cables respectively in the form of a round cable. The ribbon cable and the round cable can be wound and unwound in opposite directions onto different regions of the outer drum surface. The apparatus is arranged in a first part of a device which has a second part with electrically operated components, the second part being displaceable relative to the first part. The ribbon cable electrically connects the two parts of the device to each other. Respective ends of the ribbon cable and the round cable are secured at opposite ends of the second part of the device. Given exertion of a tensile force on the ribbon cable by displacement of the two parts of the device relative to each other, the ribbon cable is unwound from the rotatable drum, and the round cable is wound onto the drum, and given exertion of a tensile force on the round cable by opposite displacement of the two parts of the device relative to each other, the round cable is unwound from the drum, and the ribbon cable is wound onto the drum. A spring via which the round cable end is secured at the other part of the device causes a constant tensile force to be exerted on the round cable and thus on the ribbon cable, so that this is wound onto the drum with a slight initial tension.
In order to enable the winding and unwinding of the ribbon cable at all (the ribbon cable is connected at its other end to an energy supply and to a control and signal processing unit, for example) a region of the ribbon cable is wound around the inner drum surface in a spiral surface (helix). The shell surfaces of the two hollow cylindrical drums each have an opening through which the ribbon cable is conducted. The ribbon cable is first conducted into the region between the drum surfaces through the opening of the shell surface of the inner drum via a side opening of the inner drum, is wound in spirals about the inner drum and is conducted to the outside through the opening of the shell surface of the outer drum. The region of the ribbon cable located between the drums is secured at the inner drum surface and outer drum surface with its sectional ends such that given rotation of the outer drum around the inner drum the ribbon cable is wound onto the shell surface of the outer drum, or is unwound therefrom. Given winding or unwinding of the ribbon cable onto or from the outer drum, the spiral formed by the region of the ribbon cable lying between the drums narrows in the direction of the shell surface of the inner drum, or broadens.
The known apparatus is only suitable for accepting a ribbon cable, which can be wound onto or unwound from the outer drum reliably--i.e. without loop formation. A disadvantage is that ribbon cables are expensive and have a high space requirement in winding onto a drum.